Alarm constant then engine dies 4.3L Mercruiser

Been searching on the forums for some time and can't quite find my specific problem... though it has helped me rule out some things now I'm stumped.
Here are the specs: 1994 Mercruiser 4.3L V6 Thunderbolt LX Alpha one genII sterndrive.

What happend: recently bought boat on inspection it had a little bit too much oil on the dipstick but not too high. Boat ran fine, initially it idled a little high adjusted it, ran like a champ for about two weeks. Then took boat out for memorial day weekend putting around lake and tubing. About 1.5 hours in alarm buzzer sounds then oil pressure and temperature gauges bottom out engine is still running so I head back to dock almost make it when engine dies. I open it up doesnt seem like it is overheating so I start her back up and limp a few hundred feet and dies again. Finally make it back to dock and trailer it up, I get home get on the message board and start looking for solutions. I find that the alarm is the result of one of three things low engine oil (checked readings still a little high) low drive oil (readings are normal) high temperature (feels normal).

What I tried to fix alarms: Temp- I hooked engine up to muffs engine starts water is sucked up and comes out exahust (impeller works)
Oil - I removed excess engine oil, since all fluid levels were normal I moved on to checking sensors and switches. I wasn't quite sure on a couple (only got 10v on oil pressure switch) so I have replaced both the oil pressure switch and the pressure sensor. Engine runs a little longer but still dies after about a minute and alarm still sounds even after engine is running and still no readings on pressure or temperature gauges. I checked the gauges they are receiving power and register current when key is turned in ignition.

Help Im stumped!!!

Re: Alarm constant then engine dies 4.3L Mercruiser

How much excess engine oil we talking about? Cup full or a gallon? Makes a huge difference. Were the lifters rattling? engine making noise?

Was the oil milky? Did it smell like gas?

Your voltage checks, were you checking for voltage or voltage drop? HUGE difference. Where did you put the meter leads when you did the tests

Temp may be a completely different problem.

Re: Alarm constant then engine dies 4.3L Mercruiser

Don S said:

How much excess engine oil we talking about? Cup full or a gallon? Makes a huge difference. Were the lifters rattling? engine making noise?

Was the oil milky? Did it smell like gas?

Your voltage checks, were you checking for voltage or voltage drop? HUGE difference. Where did you put the meter leads when you did the tests

Temp may be a completely different problem.

Click to expand...

Excess oil: Id say about a quart. no noticible noise. Not milky a little opaque but doesnt look like there was water mixed. checked for voltage had leads on positive and the other to ground checked for voltage accross the switch then checked resistance when it was powered off either way I replaced both the oil switch and pressure sensor. I pulled the brown wire off of the oil pressure switch and the alarm stops but im pretty sure i was just interupting the circuit. I reconected it and it came back on even with the new switch. thanks for the prompt response.

Re: Alarm constant then engine dies 4.3L Mercruiser

Running for a minute then dying sounds like a fuel pump problem. Those engines run an electric pump, and the power for it runs through an oil pressure switch, but that switch is bypassed during cranking, so you get a belly full of petrol during cranking, then the carb runs dry, crank it again and you get another minutes worth of fuel.

Get a mechanical oil pressure gauge and check to see exactly would pressure you have.

Chris...